The invention pertains to monitoring systems. More particularly, the invention pertains to ambient condition monitoring systems such as fire alarm systems.
Region monitoring systems have been found to be useful when installed in buildings to monitor various on-going conditions in one or more regions of the building. Examples of these include fire alarm systems and burglar alarm systems. In addition to such systems which are usable in commercial or industrial establishments, it has been recognized that such systems, in an appropriate form, can be usefully installed in residences or small non-residential buildings.
Known residential alarm systems, in one form, include a common control element coupled by a hardwire communications link to a plurality of spaced-apart electrical units. The electrical units can include, for example, smoke detectors, intrusion detectors or the like. The electrical units can also include, if desired, output circuitry to energize alarms or to generate outgoing messages for the purpose of seeking assistance such as from a remote monitoring center or the like.
Many of the known, installed, types of residential systems have exhibited relatively limited types of communication between the common control element and the detectors or other electrical units which are coupled to the cable or communications medium. For example, systems are known wherein detectors monitoring an ambient condition, exhibit an output indicative of that condition by causing a particular current or voltage to appear on or in the communications medium. In the case where the detectors are coupled to a common control element by an electrical cable, a detector exhibiting a selected state, such as an alarm state, could cause a current to flow in the cable. The control element, upon detecting that current flow is able to establish that at least one of the detectors in the system is exhibiting an alarm state.
Typically such detectors latch into an alarm state until the control element produces a reset signal. One known way of establishing a reset is to interrupt power to the communications medium which in turn causes all of the detectors and/or electrical units coupled thereto to reset themselves.
Some of the known systems utilized established two-wire communications mediums and compatible two-wire devices. Other known systems use four-wire communications mediums with compatible four-wire devices. Known systems very often have been evaluated by a certification organization for purposes of performance and reliability under predetermined conditions. Maintaining such certification limits changes that can be made to the control element as well as to the detectors or other electrical units coupled to the system.
There continues to be a need to be able to introduce additional flexibility into existing types of residential alarm systems. Preferably, such flexibility could be introduced without requiring recertification and without introducing additional installation complexity or limiting the number of devices coupled to the system. In addition, it would be preferable if any devices responsive to such expanded capabilities were also downward compatible and functioned appropriately in known installed systems.
In accordance with the invention, a control element of a monitoring system can determine if any of the devices coupled to the system are in a predefined state. This determination uses the same voltage/current characteristics that a comparable system would exhibit without this expanded functionality.
In accordance herewith, the control element includes a programmed processor as well as interface circuits for communicating, via a communication medium such as electrical or optical cable with the devices. The control element includes executable instructions for forming a status command and transmitting same to the devices in the system.
In one embodiment, the status command can take the form of a sequence of voltage pulses. Other types of status commands can be sent without departing from the spirit and scope of the present invention. The status commands only need to be compatible with the devices coupled to the medium.
In response to receiving a predetermined status command from the control element, each of the devices which is exhibiting the respective status replies substantially immediately to the control element via the medium. The form of the reply corresponds to the same signal sent by the respective device or devices to indicate another predetermined state, such as an alarm condition. Hence, if some of the devices correspond to smoke detectors, for example, the reply to the status command from the control element, from those detectors exhibiting the appropriate status, would be the same electrical signal as would be sent by the respective detector or detectors to indicate the presence of a predetermined ambient condition.
In one aspect of the invention, the reply from the device or devices exhibiting the requested status could be in the form of one or more electrical currents caused by the respective device or devices to flow in the communication medium. For example, in an alarm state, the detector or detectors that have gone into alarm might shunt the medium. Since the responding device or devices each cause a respective current to flow in the medium, the control element can detect the presence of a cumulative current reply indicative of one or more devices which is responding to the status command.
Instructions in the control element, upon detection of the cumulative reply current in the medium, determine that one or more of the devices is exhibiting the respective status. The magnitude of the reply current is indicative of the number of devices exhibiting the status.
Alternately, instead of current, other forms of cumulative electrical or optical signals could be used. Any signal which a device exhibits in response to a predetermined condition can be used as a reply signal to a status request.
In yet another aspect, the control element can include executable instructions for forming a plurality of different commands which can be transmitted, via the medium, to the devices coupled to the system. The commands can be addressed to different conditions or states which might be present at one or more of the devices in the system. The devices need only be capable of replying with the same electrical or optical signal normally used for informing the control element of the presence of a predetermined state or condition.
The present system is particularly advantageous in that the devices are downward compatible with respect to existing previously installed, systems. Additionally, no hardware changes need be made to any of the devices nor to the control element. The control element incorporates executable instructions which provide the commands to be transmitted to the devices seeking status replies.
The devices can include executable instructions for responding to received commands with hardware which can also be used to communicate to the control element the presence of a selected predetermined condition such as fire or intrusion. The devices could also incorporate an ASIC for control.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.